In a typical cellular radio system, radio or wireless terminals (also known as mobile stations or devices and/or user equipments (UEs)) communicate via a radio access network (RAN) to one or more core networks. The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (in a Universal Mobile Telecommunications System (UMTS) network) or “eNodeB” (in a Long Term Evolution (LTE) network). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipments (UEs) within range of the base stations.
In some radio access networks, several base stations may be connected (e.g., by landlines or microwave) to a radio network controller (RNC) or a base station controller (BSC). The radio network controller supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM). Universal Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access (WCDMA) for user equipment (UEs).
In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. A number of releases for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) specification have issued, and as with most specifications, the standard is likely to evolve. The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE).
Long Term Evolution (LTE) is a variant of a 3GPP radio access technology where the radio base station nodes are connected to a core network (via Access Gateways (AGWs)) rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are distributed between the radio base stations nodes (eNodeB's in LTE) and AGWs. As such, the radio access network (RAN) of an LTE system has what is sometimes termed a “flat” architecture including radio base station nodes without reporting to radio network controller (RNC) nodes.
A currently popular vision of the future of cellular networks includes machines or other autonomous devices communicating between each other (or with an application server) without human interaction. A typical scenario is to have sensors sending measurements infrequently, where each of the transmissions would consist of only small amounts of data. This type of communication is called machine to machine (M2M) communication in the literature, or machine-type communication (MTC), in 3GPP.
M2M or MTC communication can be used for establishing communication between machines and between machines and humans. The communication may comprise transmission or exchange of data, such as measurement data, configuration information etc. or the like and/or signaling. In some applications the M2M/MTC terminals devices may be relatively small devices, for instance of the size of a conventional cellular telephone or smaller, but in other applications the devices could range in size, for example to the size of a base station. As mentioned it has been proposed that such M2M devices may be used for applications such as sensing environmental conditions (e.g. temperature reading), metering or measurement (e.g. electricity usage etc.), fault finding or error detection etc. In these applications the M2M devices may communicate relatively infrequently for a consecutive duration depending upon the type of service e.g. about 200 ms once every 2 seconds, about 500 ms every 60 minutes etc. The M2M device may also do measurement on other frequencies or other RATs.
The path loss between M2M device and the base station can be very large in some scenarios such as when used as a sensor or metering device.
In order for UEs to be able to communicate with the network, either transmit to the network or receive from the network, UEs have to listen to system information (SI) broadcast within the cell. System information includes information related to accessing the network, receiving from the network, performing cell reselection and intersystem handover among others. With LTE (3GPP LTE Rel. 11) for example system information is transmitted as 17 SI messages. There is a Master Information Block (MIB) and 16 SI Blocks (SIBs) transmitted in each cell. The MIB may, for example, be transmitted by using the Physical Broadcast Channel (PBCH), and comprises information necessary for a UE to be able to listen to the other SIs and thus be able to receive in downlink. It is therefore important that a UE be able to receive the information in the MIB.
In scenarios such as described above where the path loss between a base station and a UE, for example an M2M type device, is relatively large it can be difficult for the UE to correctly receive the signal from the base station.
One way to potentially improve the receipt of SI by UEs that suffer from a relatively high path loss is to increase the number of times that a broadcast channel is transmitted in a given period, i.e. to transmit additional repetitions of the broadcast channel, e.g. repetitions of SI information such as MIB information. Conventionally the Physical Broadcast Channel (PBCH) is transmitted once per radio frame. Increasing the number of transmissions of a broadcast channel means that the broadcast channel, i.e. MIB, may be repeated a number of times in a radio frame. These repetitions can also be combined with power boosting.
As new MIB data is transmitted on a certain timescale, which is currently 40 ms for LTE, any such repetitions have to be confined to this time window, i.e. 40 ms. The broadcast channel, e.g. the PBCH, may therefore be configured with frequent repetitions, for example every subframe, during this 40 ms time window with an aim to enhance the reliability of its reception at the UE. If MIB were transmitted at every Transmission Time Interval (TTI) and repetitions were combined with some power boosting of the PBCH then an improvement in link budget of the order of 15-20 dB could be achieved compared to an LTE scheme without such repetitions. Thus the SI may be repeated a number of times which is relatively high, e.g. in the order of several dozens.
However such a transmission scheme would use up the 6 central resource blocks, which could be necessary for other purposes. Thus the overhead associated with such MIB transmission may be unacceptable in at least some applications.
To reduce the overhead associated with such intense MIB repetition the repetition may be implemented such that increased or intense SI repetition does not occur constantly but only within certain time windows. In other words a period of increased repetition of the MIB, i.e. increased repetition of the physical broadcast channel, may occur periodically or sporadically interspersed with periods without such increased repetition. These time windows of increased PBCH repetition, which may be combined within PBCH power boosting, might occur either periodically, or in an event trigger manner.
Additionally the structure of system information transmission could be modified. For example the time window for MIB could be modified so that so as to allow repetition of MIB for longer timescales, for example 80 or 160 ms. Power boosting, for instance power spectral density (PSD) boosting could also be applied if the number of repetitions within the time windows (before the MIB changes) is not sufficient to achieve a desired link budget. In changing the structure of the SI it would also be possible to keep SI content which is necessary for M2M/MTC in one physical channel, which could be a channel that already exists in LTE, or a new defined physical channel.